Releasable mounting and method of placing an oriented array of devices on the mounting

ABSTRACT

An oriented array of small, fragile electrical devices such as beam lead transistors or integrated circuits, partially embedded in wax, are removed from the wax and transferred to a releasable mounting without disrupting the orientation of the devices. The releasable mounting comprises a plate with a layer of silicone rubber or resin which exerts a suction or vacuum holding force on the array of oriented devices.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of application Ser. No. 232,735, filed Mar. 8, 1972,now U.S. Pat. No. 3,899,379 which is a division of application Ser. No.64,898, filed July 30, 1970, now U.S. Pat. No. 3,690,984 which is adivision of application Ser. No. 729,859, filed Apr. 10, 1968, now U.S.Pat. No. 3,632,074 which is a continuation-in-part of application Ser.No. 673,900, filed on Oct. 9, 1967, now abandoned.

BACKGROUND OF THE INVENTION

This invention is particularly adapted for use in the manufacture ofsmall, fragile semiconductor devices or integrated circuits of theso-called beam lead type. Examples of these beam lead devices aredisclosed in M. P. Lepselter U.S. Pat. Nos. 3,287,612 and 3,335,338. Theinvention is adapted to be used in conjunction with picking up, holdingand maintaining orientation of small articles, but will be particularlydescribed with respect to beam lead transistor devices which comprise asemiconductor body on which leads bonded as an integral part of thedevice extend from the body like cantilever beams to form bothelectrical and mechanical connections to a header or circuit patternformed on a substrate. These beam leads are essentially of gold which iselectroplated onto a semiconductor body which will be hereinafterdesignated a wafer.

A typical beam lead device is very minute, the leads being only 10microns thick, 3 mils wide and 9 mils long while a square wafer body isonly 2 mils thick and 18 mils wide.

In batch manufacture of these fragile devices, a plurality of arrays ofbeam leads are electroplated to extend from a number of active or dopedareas formed in a slice or sheet of semiconductor material such assilicon. The slice is secured to a mounting plate with wax so that thebeam leads are embedded in the wax. The nonwaxed surface of the slice ismasked with a photosensitive resist to expose the area betweenindividual transistors and these exposed areas are etched to separateand form a plurality of individual beam lead transistor devices.

Heretofore, the resist and wax were removed by use of suitable solvents.This treatment resulted in a loss of the orientation of the transistordevices on the mounting plate, or if the devices were left in anoriented array on the plate, there was no way of moving the plate fromthe fabrication location to another manufacturing location without lossof the device orientation. A number of mechanical apparatus of thevibratory or shaker type were developed and tried in an attempt toregain orientation of the devices to enable subsequent manufacturingoperations to be performed on the devices. However, these apparatusproved less than satisfactory because of damage to the beam lead deviceor slow operating capabilities in providing a supply of devices for thesubsequent manufacturing operations. These subsequent operations mayinclude testing of the devices or the assembly and bonding of thedevices into integrated circuit modules. For economic mass production,it would be advantageous if the devices could be transferred from thebatch fabrication location in oriented array to permit facile handling,feeding or loading of the devices into automatic testing or bondingmachines.

The need for maintaining device orientation without individual handlingof the devices may be further appreciated by noting that it is verydifficult to transfer beam lead devices of this minute size withoutdamaging or bending the leads, or without chipping or scratching thewafers.

SUMMARY OF THE INVENTION

The present invention contemplates new and improved methods of handlingbeam lead devices during manufacturing operations, while maintainingdevice orientation and decreasng the likelihood of damage to thedevices. More particularly, in one embodiment of the invention the beamlead devices, partially embedded in a wax layer on a mounting plate, arecleaned of a photoresist coating and then temporarily secured to anintermediate holding device while the wax and the mounting plate areremoved. Next, the exposed portions of the devices are pressed against acarrier plate which exerts an attractive vacuum force on the devices.Finally, the intermediate holding device is removed leaving the devicesin the original orientation on the carrier plate. The attractive forceexerted by the carrier plate is sufficient to hold the devices in theoriginal orientation during shipment to another manufacturing locationwhere each device can be easily removed from the carrier plate andbonded or connected to a circuit module.

The invention also contemplates a carrier, or a mounting plate coated orotherwise constructed of, or provided with a layer of, silicone rubberor resin which engages and applies a vacuum or suction holding force tothe individual transistor devices or other articles. This vacuum holdingforce is sufficient to maintain device orientation during subsequenthandling or transfer, but yet the force is small enough to permit easyremoval of the devices by use of a vacuum pickup or a pair of tweezers.The pressure sensitive vacuum holding properties of the carrier may becontrolled by changing such parameters as the size of the contactedarea, the surface roughness or configuration and the thickness of thecoating or carrier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a greatly enlarged perspective view of a beam lead transistordevice which may be effectively transferred from a mounting plate onto acarrier plate in accordance with the principles of the presentinvention;

FIG. 2 discloses a disc-like mounting plate having a layer of wax whichserves to partially embed an oriented array of transistor devicesfollowing device fabrication;

FIG. 3 is a perspective, sectional view, again greatly enlarged, takenalong line 3--3 of FIG. 2, showing a portion of one device embedded inwax and also disclosing a photoresist layer on a semiconductor wafer orchip of the device;

FIG. 4 is a sectional view through the array of oriented transistordevices and the mounting plate illustrating a fluid stream being appliedto remove the photoresist;

FIG. 5 shows a cross section of a fixture wherein a screen is stretchedacross the oriented array of transistor devices in preparation fortemporary securing of the transistors and the mounting plate to thescreen;

FIG. 6 is a sectional view illustrating the application of a solubleadhesive through the screen to secure the transistors to the screen;

FIG. 7 depicts the immersion of the transistor devices, the screen and apart of the fixture in a solvent that acts to dissolve the wax;

FIG. 8 shows the fixture reassembled with the dewaxed transistors urgedinto pressing engagement with a layer of silicon resin on a carrierplate in anticipation of immersion of the fixture into a tank of fluidsolvent which acts to dissolve the temporary adhesive;

FIG. 9 shows the carrier plate vacuum holding an array of transistors inanticipation of subsequent handling or transportation;

FIGS. 10, 11 and 12 illustrate an alternative embodiment of theinvention wherein ice is used as an intermediate holder during thetransfer of articles from a mounting plate to a pressure sensitivevacuum holding mounting;

FIGS. 13, 14, 15 and 16 illustrate a method of the invention whereinarticles are selectively transferred from a mounting plate to anintermediate holder constructed of a peelable adhesive, and then to apressure sensitive, vacuum holding carrier;

FIG. 17 illustrates additional aspects of the method of the inventionwherein beam lead devices embedded in wax directly transferred onto apressure sensitive vacuum holding layer;

FIGS. 18, 19, 20, 21 and 22 graphically depict a further application ofthe principles of the invention wherein individual transistor devicesare fabricated to be releasably supported by individual plugsconstructed of pressure sensitive, vacuum holding material which acts asa peelable adhesive;

FIG. 23 shows a carrier having depressions formed in its surface tolimit the pressure sensitive vacuum holding properties of the carrier;

FIGS. 24, 25 and 26 illustrate a method of separating a frangiblesubstrate and retaining the separated substrate on a pressure sensitive,vacuum holding carrier; and

FIGS. 27 and 28 illustrate a method of relieving the holding force on anarticle by applying a swelling agent to a support constructed ofpressure sensitive, vacuum holdng material;

FIG. 29 is a cross-sectional view illustrating an alternative embodimentof the fixture shown in FIG. 5, wherein a screen is stretched across theoriented array of transistor devices positioned on a movable pedestalhaving a nonplanar surface in preparation for temporary securing of thetransistors and the mounting plate to the screen;

FIG. 30 is an enlarged cross section of a portion of the fixture shownin FIG. 29 illustrating the manner in which the screen is spaced apredetermined distance from the remainder of the fixture;

FIGS. 31, 32 and 33 graphically depict a further application of theprinciples of the invention wherein the distance between individualtransistor devices of an array thereof is increased by stretching asubstrate on which the array is temporarily held and, wherein theseparated devices are transferred to a pressure sensitive, vacuumholding carrier.

DETAILED DESCRIPTION

Referring to FIG. 1, there is shown a beam lead transistor device 10comprising a semiconductor body, or wafer, 11 having a doped or activearea 11' in communication with three beam leads 12 extending incantilevered fashion as integral parts of the wafer. One embodiment ofthe invention will be explained with respect to the handling of beamlead transistor devices. As previously explained, a great multitude ofbeam lead transistor devices 10 are simultaneously fabricated from asingle silicon slice, e. g., 1200 devices may be formed from a slicehaving a diameter of 1 inch. Upon separation of the individualtransistor devices, they are maintained in orientation due to the factthat the slice was originally secured by a pliant cement, such as wax 13(FIGS. 2 and 3), to a sapphire or aluminum oxide or glass mounting disc14. The pliant cement is selected to be removable or releasable upon theapplication of heat and/or a solvent. It is desired in the practice ofthis embodiment of the inventive method that the transistor devices 10be removed from the wax 13 and placed on a carrier which can betransported to another manufacturing area for subsequent processing ofthe transistor devices.

Referring to FIG. 3, it will be noted that the beam 12 is fully embeddedin the wax 13 while the transistor wafer 11 is fully exposed except foractive area side 11'. During the fabrication of the individualtransistor devices, each was masked with a photoresist 16 to leaveexposed the intervening spaces between the individual devices. Theexposed intervening surfaces were etched, thus leaving an array ofseparated, individual transistor devices embedded in wax, as shown inFIG. 2. The resist 16, which may be of the type sold by the EastmanKodak Company under the trade designation KTFR, may be removed byprojecting a pressurized fluid stream 17 (FIG. 4) from a nozzle 18 inthe manner taught in W. R. Wanesky U.S. Pat. No. 3,515,607. The fluidstream 17 works its way under the photoresist layer 16 to peel theresist layer from the wafer 11, leaving the beam lead transistor devices10 embedded in the wax 13 as depicted in the right-hand portion of FIG.4.

Considering now the steps in removing the wax, the sapphire mountingplate 14, along with the wax embedded devices 10, are placed on a flatpedestal 21 (see FIG. 5) projecting from a circular base 22 of a fixture23. The fixture includes an annular ring 24 across which is stretched afine mesh screen 26, e. g., stainless steel 230 mesh screen. The screenmesh should be selected so that several openings are presented to eachtransistor device while being of sufficient size to allow for the flowof liquid therethrough. The annular ring 24 is assembled on the base 22and may be secured thereto by fasteners 27, which are illustrated aswing bolts extending through bores 28 and into threaded apertures 29formed about the peripheral area of the base 22. In the practice of thisstep of the method, it is not necessary to draw up the wing bolts 27, itbeing sufficient to merely place the screen 26 over the exposedtransistor devices 10. As shown in FIG. 6, an adhesive or hardenablematerial 31, such as cellulose nitrate or cellulose acetate, is nowsprayed or otherwise spread over the screen 26 to embed and secure thewafers 11 in place. The wafers 11 are thus cemented in the originalorientation to the screen which serves as an intermediate holder in thetransfer process. A brush 32, or pallet spreader, may be utilized tofacilitate the even distribution and flow of the cellulose nitratethrough the screen and about the wafers 11.

Next, it is desired that the wax 13 be removed to release the sapphiremounting plate 14. First, the wax 13 may be softened by application ofheat allowing the mounting plate and a good portion of the wax to belifted or peeled from the transistor devices 10. The removal of theremaining wax may be accomplished, as illustrated in FIG. 7, byimmersing the annular ring 24, the screen 26 and the adhered to orientedarray of wafers 11, along with the remaining wax 13 and the mountingplate 14, in a bath 33 of boiling trichloroethylene or other solventthat will dissolve the wax, but not the adhesive 31. Thetrichloroethylene acts as a solvent to remove the wax from thecompletely exposed undersurfaces of the devices 10, but does not destroythe bonding strength of the cellulose nitrate. Any residual wax, orother foreign particles, may be removed by applying a spray oftrichloroethylene, or other suitable cleaning fluid, to the exposedundersides of the transistor devices.

It is now desired to transfer the transistor devices 10 onto a carrierplate, or disc, 36 such as illustrated in FIG. 9. The disc 36 has alayer or film 37 of pressure sensitive, vacuum holding material, such assilicone resin of the general type sold by the Dow Corning Corporationunder the trade designation "Sylgard 182." Investigations revealed thatthe silicone resin possesses the property of releasably holding a smoothsurface, nonporous device when such a device is pressed against theexposed surface of the resin.

The coated disc 36 is placed on the pedestal 21 (see FIG. 8) and thering 24 is secured in the fixture by tightening the wing bolts 27. Thedewaxed beam lead transistor devices 10 are now sandwiched between thesilicone resin layer 37 and the cellulose nitrate adhesive 31. The bolts27 are drawn up to tension the screen 26 and force the undersides of thebeam leads 12 into intimate contact with the surface of the siliconeresin layer 37.

In a more preferred embodiment the coated disc 36 is placed on a movablepedestal 103 (see FIG. 29) which is in a lowered position. The ring 24is placed in position on the lower portion 104 of a second fixture 105and rests on a spring-loaded plungers 106 of screw assemblies 107. Theassemblies 107, each of which comprises a plunger 106 and screw 112having a spring 113 mounted therebetween, are adjusted up or down toobtain a predetermined space 108 (see FIG. 30) between the ring 24 andthe lower portion 104 of the fixture 105. Having been positioned toobtain the desired space 108, each assembly 107 is locked in place by anut 109. The pedestal 103, with the coated disc 36 thereon, is raisedfrom its lowered position until the coating 37 just touches the devices10 attached to the screen 26. At this point, the pedestal 103 is lockedto the lower portion 104 of the fixture 105 by means of a wing screw110.

The space 108 is chosen so that when wing screws 27 (see FIG. 29) aretightened sufficiently to draw the ring 24 against the lower portion 104of the fixture 105, the screen 26 will not be deformed beyond itselastic limit.

As illustrated in FIGS. 29 and 30, the top surface of pedestal 103 maybe slightly convex or coneshaped with the center of the surface 111, inany case, being elevated several thousandths of an inch above the outerperiphery thereof. In addition, it is preferred that the elevatedportion of the surface 111 include a flat area to add stability to thedisc 36 when the ring 24 is unclamped. When the ring 24 is brought intocontact with the lower portion 104 of the fixture, the screen 26 isdrawn taut exerting a downward force on the disc 36 sufficient to causeit to take an approximately spherical shape, but not sufficient to causethe disc to fracture. Because the screen 26 is pulling down on the nowdome-shaped or spherical surface of the disc 36, there exists downwardcomponents of force which press devices 10 anywhere on the screenagainst coating 37. This brings the underside of beam leads 12 intointimate contact with the surface of the silicone resin layer 37 andassures the transfer of all devices 10, particularly smaller ones.

Regardless of whether a flat pedestal 21 or a nonplanar, movablepedestal 103 is employed, the assembled fixture (23 or 105,respectively) is now immersed in a bath of solvent 38; e. g., acetone,to dissolve the cellulose nitrate. The fixture is removed from the bathand the wing bolts 27 loosened to remove the screen 26. The disc 36 maynow be lifted and the beam lead transistors 10 will remain on thesurface of the silicone resin layer 37 in the original orientation shownin FIG. 2. In addition, it will be noted that the fragile beam leads 12are fully supported by either the wax 13, the intermediate cellulosenitrate adherent 31, or the silicone resin layer 37 during the varioussteps of the process, thereby substantially eliminating the possibilityof bending or otherwise damaging the beam leads.

The carrier disc 36 may be constructed of a heat resistant glass with a0.005 to 0.001 silicone resin or rubber film. The glass disc is firstprimed for good adhesion of the silicone resin. When silicone resin isto be used as the film, then the primer may be of the type sold underthe trade designation Sylgard primer by the Dow Corning Company and whensilicone rubber is used, then the primer may be of the type sold underthe trade designation "Silastic 1201" primer by the Dow Corning Company.The film coating may be cast on the surface of the glass disc and then athin, flexible cover, with the surface of the desired roughness, isplaced against the coating after which the resin is cured. The surfaceof the silicone layer will be an exact reproduction of the surface ofthe cover which is peeled away after curing. It has been furtherdiscovered that the surface roughness is directly related to the abilityof the silicone resin to hold objects pressed against the surface; thesmoother the surface, the greater the holding ability. It has also beenfound that thicker, softer layers of silicon resin or rubber exhibitgreater holding abilities. Experiments have shown that porous objects,such as paper, do not adhere to the silicone resin surface which leadsto the theory that a vacuum is produced between the object and thesurface of the silicone resin, so that, when an object is pressedagainst the surface, it displaces the air therebetween.

When an oriented array of beam lead transistor devices are transferredto the silicone resin coated disc 36, the disc may be transportedwithout loss of device orientation. The use of a transparent, heatresistant glass disc 36 with a silicone resin layer has the addedadvantage in that the entire assemblage is transparent, thus permittingvisual inspection of the underside of the beam lead transistor devices10. The transistor devices may be removed from the carrier by a vacuumprobe, or by use of tweezers, and advanced into a bonding machine forsubsequent connection to a circuit module or onto a header.

In the alternative, the disc 36 may be coated with silicone rubber, suchas Silastic silicone rubber manufactured by the Dow Corning Company. Thesilicone rubber is opaque, but it does not have the same pressuresensitive, vacuum holding properties exhibited by the silicone resin.Further, either the silicone resin, or the silicone rubber, may beformed on the disc 36 by placing small amounts of uncured resin orrubber on the disc and then spinning the disc at a high speed, such as8000 rpm. Upon uniform spreading of the resin or rubber over the surfaceof the disc, the spinning is stopped, and the resin or rubber is allowedto completely cure and adhere to the disc 36. It will be observed thatin both instances, only thin, film-like layers 37 of holding materialare applied to the carrier disc. Film thickness of the magnitude of0.0005 to 0.001 have proved effective in holding the oriented devices 10during transportation, while allowing easy removal of tweezers or avacuum pick up at the subsequent fabricating or assembly location.

Attention is now directed to FIGS. 10, 11 and 12 for consideration of asecond embodiment of the invention. Again, the mounting disc 14 isplaced in the fixture 23 so that the screen 26 is resting on the tops ofthe transistor devices 10. In this instance, the photoresist layers 16may be retained on the transistor wafers 11. The fixture 23 is nowsuccessively immersed in solvents that act to dissolve the wax 13 andthe photoresist 16. Successive immersions in a resist etchant (such assold under the trade designation J-100, by the Indust-Ri-Chem Labs,Richardson, Tex., trichloroethylene, and acetone remove both thephotoresist 16 and the wax 13, leaving the device 10 retained by thescreen 26 on the mounting plate 14. Next, a hardenable or solidifiableliquid, such as a few drops of water 41, is spread over the screen 26 towet the screen 26 and the devices 10. The water 41 is then frozen bymoving a suitable refrigerating device into the vicinity of the water;for example, a shallow copper receptacle 42 containing dry ice 43. Thewing bolts 27 are now removed and the upper, annular ring section 24 islifted to enable the removal of the mounting plate 14 to expose theundersurfaces of the devices. This mounting plate may be removed by thesimple gripping with and manipulation of a pair of tweezers.

It is now desired to again transfer the ice-encased transistor devices10 to a carrier plate 36 having a layer of pressure sensitive, vacuumholding material 37. As shown in FIG. 12, the carrier plate 36 ismounted on the pedestal 21 of the fixture 23 and the annular ring 24 isreassembled to move the transistor devices 10 against the pressuresensitive, vacuum holding layer 37. The beam leads 12 are forced intointimate engagement with the layer 37 upon retightening of the wingbolts 27. The ice 44 is melted by bringing a suitable heating fixture 46into proximity with the fixture 23. The ice melts and flows from thepedestal 21 and the remaining moisture is evaporated, leaving the screen26 urging the devices 10 toward the layer 37. Again, the pressuresensitive, vacuum holding layer 37 will exert a holding force on thebeam leads 12 so that when the screen 26 is removed, the transistordevices 10 are arrayed on the layer 37 in the original orientation asdepicted in FIG. 9.

It is to be understood that in the practice of this embodiment of themethod, the resist layer 16 can be removed by a fluid blast as depictedin FIG. 4. In this instance, there is no need to immerse the assembledfixture 23 in a solvent for removing the photoresist 16, an immersion inboiling trichloroethylene being sufficient to dissolve the wax and cleanthe devices 10.

Referring now to FIGS. 13, 14, 15 and 16 for an understanding of afurther embodiment of the invention wherein the transistor devices arenot only transferred from the mounting plate 14 onto the carrier plate36, but also those transistor devices 10 found to be defective areremoved and not transferred onto the carrier plate. Again, the devices10 are embedded in a wax 13 on the mounting plate 14. The devices 10 canbe visually checked or electrically tested to determine which devices inthe array are defective. An intermediate holder in the form of a card 51of a suitable smooth plastic, such as a polyester condensation productof ethylene glycol and terephthalic acid sold under the trade nameMylar, by E. I. du Pont de Nemours & Company, is punched with acoordinate array of apertures 52 corresponding to the devices 10 thatpassed inspection. It will be noted that no apertures appear in theaperture array which correspond to the defective devices in the devicearray cemented in the wax 13.

The card 51 is now positioned, as shown in FIG. 15, to align theapertures 52 with the satisfactory devices 10. In this instance,pressure sensitive, vacuum holding material acting as a peelable,adhesive is spread over the card 51, and through the apertures 52 intointimate engagement with the exposed top surfaces of the devices 10 toform an intermediate adherent layer 53. This layer is cured and theassemblage is then immersed in boiling trichloroethylene to dissolve thewax 13. Those devices 10 not contacted by the peelable, adhesive layer53 are released and dropped into the tank of solvent. The mounting plate14 is also released leaving the devices 10 clinging to projections 54extending from the adherent, peelable layer 53. If any of the defectivedevices 10 are not washed away during the immersion in the solvent, theymay be brushed from the card, leaving the satisfactory devices clingingto the projections 54. The card 51, with the layer 53 and thesatisfactory devices 10, is then pressed against a layer of pressuresensitive, vacuum holding material 37, as illustrated in FIG. 16. Thecard 51 is held and the layer 53 peeled away to withdraw the projections54 from contact with the devices 10. The satisfactory devices 10 are nowheld, in their original orientation, on the pressure sensitive, vacuumholding layer 37 of the carrier plate 36.

In another application of the principles of the invention, a carrierplate 61, (see FIG. 17) is provided with a thin layer 62 of pressuresensitive, vacuum holding material, such as silicone resin, and then alayer of liquid wax 63. A silicon slice 64, with the beam lead 12 sidedown, is pressed into the wax. As previously described, the slice isprovided with a resist pattern 66 overlying the individual transistordevices 10. Again, the intervening exposed area (shown in dashed lines)of the slice 64 are etched away. Now, the carrier plate 61, with thewax-held devices 10, is placed on the pedestal 21 (see FIG. 5) of thefixture 23 and the screen 26 drawn down by tightening the wing bolts 27.This assemblage is immersed in a bath of boiling trichloroethylene todissolve the wax. Upon removal from the bath, the annular ring 24 isremoved leaving the oriented array of beam lead devices 10 held on theunderlying silicone resin layer 62. Again, the orientation of thedevices is not disrupted by subsequent transport and permis removal ofthe devices by a vacuum pickup probe at an assembly station.

Referring now to FIGS. 18, 19, 20, 21 and 22, there is illustrated amodified method of fabricating individual transistor devices 10 so thateach device is releasably supported and held on an individual plug ofsilicone resin or silicone rubber. First, a carrier plate 70 (FIG. 18)of ceramic is constructed and formed with a plurality of frusto-conicalopenings 71. Next, a layer of wax 72, such as glycol phthalate is spreadover the plate 70 to cover the upper surface of the plate andincidentally fill the openings 71. A silicon slice 73 with arrays ofbeam leads 12 is pressed into the wax to imbed the leads with thecenters of the devices over the centers of the upper extremities of theopenings 71. The wax flowing into the hole 71 is now removed bydirecting a spray 74 (see FIG. 19) of solvent against the underside ofthe carrier plate 70. The spray also removed a portion of the way layer72 to expose areas 75 on the underside of the slice.

The next operation is to draw silicone resin or silicone rubber into theconical openings 71 to engage the now exposed undersurface areas 75 ofthe slice 73. The carrier plate 70 is inverted as shown in FIG. 20, anda layer 76 of uncured silicone resin or silicone rubber is spread overthe top surface of the now inverted plate. Some resin 76' flows into theopenings 71 but these openings are not completely filled because of therelatively high viscosity of the uncured resin and the small dimensionsof the openings. As shown in FIG. 20, the plate 70 is placed in a vacuumchamber 77. Vacuum is developed within the chamber 77 and the air in theopenings 71 is drawn into the chamber to bubble the resin, as depictedby the dash outline 76". The bubbles 76" will burst after limitedexpansion so that the vacuum will now be impessed within the openings71. Again some of the silicone resin flows into the openings which arenow subject to the same vacuum that appears in the chamber 77. However,these openings are still not completely filled.

The carrier plate 70 is removed from the vacuum chamber 77 whereuponambient air pressure acts on the fluid silicone resin 76 to force theresin into the openins 71. The resin completely fills the openings 71(see FIG. 21) and contacts the exposed surfaces 75 of the slice 73. Thesilicone resin is cured. From an inspection of FIG. 21, it will be notedthat small projections 78 extend from the openings 71 through theopenings formed by the removal of the wax 72. The ends of these smallprojections abut and exert a holding force on the exposed surfaces 75 ofthe slice.

In the manner previously described, the slice 10 is masked with resistpatterns over the individual transistor device areas. Again the slice isetched to form the individual transistor devices 10. Upon subsequentremoval of the resist and the remaining wax by immersion in suitablesolvents as previously described, the individual transistor devices 10will be held, as shown in FIG. 22, on the end faces of the projections78 extending from the now formed frusto-conical plugs 79 positioned inthe openings 71. Each individual transistor device may be removed withtweezers or a vacuum probe. In the alternative, the remaining layer 80of silicone resin may be peeled from the underside of the carrier plate70 to remove the plugs 79 from the openings leaving the transistordevices freely supported and in the original orientation on the uppersurface of the carrier plate 70.

Considering a still further feature of the invention, it was discoveredthat the holding effect of the pressure sensitive, vacuum holding layercan be reduced by forming a great number of small, shallow pocketsseparated by ridges in the surface of the layer. As shown in FIG. 23, alayer 81 is provided with a coordinate array of square pockets 82separated by ridges 83, in one direction, and equal length ridges 84 inthe transverse, orthogonal direction. The pockets may be tapered, 5 milswide and 1 mil deep. When a beam lead device 10, having dimensions ofsufficient magnitude to span several pockets, is pressed against such apocketed layer 81, the initial holding force was found to besubstantial, precluding easy separation of the device 10 from the layer81. However, after a few minutes, this initial holding force wasdissipated, permitting the easy removal of the device 10 by manipulationof a pair of tweezers or a vacuum probe. It is believed that thereduction of holding force is due to air leaking into the holdingcavities or pockets 82.

Attention is directed to FIGS. 22, 23 and 24 for a consideration of afurther application of certain principles of the invention. In thisinstance, a slice 91 of frangible semiconductor material of the typeused in the manufacture of transistors, is scribed or scored to provideorthographic grooves 92 and 93 to define individual transistor wafers94. The scribed slice 91 is placed between a carrier sheet 96 ofpressure sensitive, vacuum holding material and a flexible plastic sheet97 which does not possess the property or ability to hold articlesplaced thereon. The plastic sheet may be constructed of a polyestersheet such as sold under the trade designation Mylar, by the E. I. duPont de Nemours & Company. The sheets 96 and 97 and the interveningslice 91, are subject to flexing forces to sever the slice along thescored grooves 92 and 93. The slice, fractured along the scored lines,leaves the individual wafers 94 adhered to the pressure sensitive,vacuum holding sheet 96. The plastic sheet 97 is removed, leaving thewafers 94 in a coordinate array that is held to the carrier sheet 96.

A still further feature of the invention contemplates the transfer ofobjects, such as transistor devices 10, from a first sheet of pressuresensitive, vacuum holding material onto a second sheet of such materialby merely providing the second sheet with greater holding ability. Theseincreased holding abilities can be attained by providing the secondsheet with either a smoother surface, or by making the second sheetthicker than the first sheet. In both instances, if the top and bottomsurfaces of the transistor devices are equally smooth, then the pressingof the second sheet against the transistor devices on a first sheetresults in a transfer and adherence of the devices to the second sheetupon subsequent separation of the sheets.

The holding force exerted by the pressure sensitive, vacuum holdingmaterial, may be relieved by spraying the exposed surface about thearticle with trichloroethylene. More particularly, referring to FIG. 27,there is shown an article 98 such as a transistor device supported on acarrier or layer of pressure sensitive, vacuum holding material 99(silicone resin or silicone rubber). The exposed surface of the layer 99about the article 98 is sprayed with trichloroethylene and the sprayacts to expand or swell up the material 99 so that the material adjacentthe peripheral edges 101 of the article actually lifts the article fromthe original surface in the manner illustrated in FIG. 28. The article98 acts as a mask so that the bulk of the area underneath the article isnot affected by the trichloroethylene. When the trichloroethyleneevaporates, or is removed, the layer 99 returns to its original size.However, the article is now held by significantly smaller force therebyfacilitating easy removal of the article. The smaller force is due tothe fact that the force urging the article into engagement is determinedby the weight of the article. Of course, a strong holding force can bere-established by pressing the article against the surface of the layer.

An article, such as article 98, may be transferred from a first layer ofpressure sensitive, vacuum holding material to a second layer by firstspraying the first layer with trichloroethylene to reduce the vacuumholding force underneath the article and then pressing an untreatedsecond layer of pressure sensitive, vacuum holding material against thearticle. When the layers are separated, the article will cling to thesecond layer.

A still further feature of this invention contemplates the transfer ofobjects, such as transistor devices 10, from a resilient stretchablesubstrate 102 (see FIGS. 31 and 32) which has been stretched to increasethe spacing between the devices, While the substrate 102 is in itsstretched condition, a disc 36 having a coating of silicone rubber orresin 37 thereon is brought down over the separated devices 10 and intocontact therewith, as illustrated in FIG. 33. A further description ofthe above described method of transferring separated devices 10 is setforth in U.S. Pat. No. 3,448,510 issued to J. R. Bippus and A. F.Johnson, which is assigned to the assignee of this application. Thesubject matter of that patent application is incorporated herein byreference.

It is to be understood that the above-described methods, arrangements ofapparatus, and composition of elemental parts are simply illustrative ofan application of the principles of the invention and many othermodifications may be made without departing from the invention.

What is claimed is:
 1. A method of reducing the holding force on an article supported by a layer of pressure sensitive, vacuum holding material selected from the group consisting of silicone rubber and silicone resin, which comprises:applying a spray of trichloroethylene to the surface of the layer to swell the layer about the article to lift the article; and then removing the trichloroethylene to reduce the swelling to again hold the article against the layer with a reduced force. 